Chemical milling or chemical etching refers to the process of removing undesired material from a part, or otherwise exposing a surface of a part. Chemical etching typically occurs as a precursor process to further processing of a part. In typical chemical etching processes, a part has a portion of its surface masked from unwanted surface material removal that occurs during the chemical etching. The masked area of the part represents the portion of the part surface that will remain unchanged from the chemical etching process. The unmasked areas on the part, therefore, will be exposed and subject to the effects of the chemical etching process. For the purposes of the present disclosure, the terms “chemical milling” and “chemical etching”; and “milling” and “etching” are understood to be equivalent terms.
Typical chemical etching procedures require the presence of a chemical bath into which a part is placed or immersed. The chemical bath comprises chemicals used to “etch” or change the exposed part surface, usually through material removal from the exposed surfaces. The etching chemicals are typically hazardous to use and dispose of. Typical chemical etching baths comprise etching chemicals such as, for example, nitric acid, hydrochloric acid, hydrofluoric acid, etc. Industrial sized chemical etching baths can range in volume from about several hundred gallons up to several thousand gallons. Known chemical etching processes employing a large volume chemical etching bath therefore create a significant and expensive waste disposal issue when the baths become depleted and otherwise require replacement.
In addition, known chemical etching methods become undesirable if the part to be etched is a “high risk” part, where any accidental and unwanted exposure of a part surface to a chemical bath can result in part damage and lead to significant material waste due to part rejection. This is of particular, though not exclusive, concern with parts comprising precision milled holes and pathways, etc.
A chemical etching process that eliminates the risk of unwanted chemical etching on particular part surfaces, while also reducing part waste and also reduces the attendant costs for part waste and chemical bath maintenance and disposal would be highly advantageous.